1. Field of the Invention
This invention relates to a sheet feeding apparatus for feeding sheets and, more particularly, to a sheet feeding apparatus for feeding recording media in a recording apparatus having a function such as a printer, a photocopier, a facsimile machine, or the like.
2. Description of Related Art
Recording apparatuses having a function such as a printer, a photocopier, a facsimile machine, or the like, and recording apparatuses used for output devices for hybrid electronics apparatuses such as computers and word processing apparatuses or workstations are structured to record images on recording media such as sheet papers and plastic thin plates based on image information. The recording apparatuses can be categorized, based on the recording method, into the inkjet type, the wire dot type, the thermal type, the laser beam type, or the like.
In a recording apparatus of a serial type using a serial scanning method in which a main scanning is made in a direction intersecting with a feeding direction of the recording medium (subsidiary scanning direction), the entire recording medium is recorded by repeating the processes of recording images (main scanning) by a recording means mounted on a carriage traveling along a recording medium feeding the sheet in a fixed amount (pitch feeding) after images of one line are recorded, and subsequently recording images of the next line (main scanning) on the recording medium stopped again. On the other hand, in a line type recording apparatus which does recording only in the subsidiary scanning direction, the entire recording medium is recorded by repeating the processes of setting a recording medium at a prescribed recording position. feeding the recording medium in a predetermined amount (pitch feeding) after the one line recording is made at one time, and recording the next line at one time.
FIG. 11 shows a perspective view showing a conventional inkjet recording apparatus. In the inkjet recording apparatus, the recording medium fed by a feeding apparatus 101 is held by a platen 122 constituted such that a feeding surface in the printing area is made flat and delivered by a delivery means 133 formed on a downstream side in the feeding direction after images are formed by a recording head 124.
The delivery means 133 includes a delivery roller 134, and a special paper pressing member (e.g., a spur having a gear teeth on circumferential surface) 136d located facing to the delivery roller 134 for feeding the recording medium in pressing the recording medium through point contacts. Rotation of those members makes the recording medium fed with applied inks not yet fixed right after printing.
The delivery roller 134 is freely rotatable where each opposite end of the shaft is attached to a bearing formed at the platen 122. A recording medium feeding portion of the roller is rounded with a material such as a rubber or sponge-like material thereby rendering the recording medium hardly slip when fed.
The drive force given to the delivery roller 134 is transmitted from a paper feeding roller 132 via a transmission roller 135 attached to the platen. The transmission roller 135 is urged as to press both of the paper feeding roller 132 and the delivery roller 134 by an elastic shaft.
The spur 136 has a circumferential portion with gear teeth, which tend not to leave pressed marks or ink marks on the recording medium, so that such a spur is widely used for an inkjet recording apparatus.
The spur 136 functions for maintaining the printing quality in suppressing cockling of the recording medium in a direction perpendicular to the feeding direction when recording is made with high recording density or high duty and for protecting the recording head 124 by avoiding contacts between the recording head 124 and the recording medium.
The spur 136 is mounted on an attachment member with the elastic shaft go that the spur can move in substantially a perpendicular direction with respect to the feeding surface for the recording medium according to the thickness of the recording medium, and the attachment member may be formed with a restricting means for restricting the movement of the elastic shaft to restrict the movement of the spur 136 in substantially the perpendicular direction. This is for suppressing the movement of the spur 136 within a predetermined distance where the recording media is fed in a multiple number from the feeding apparatus 101 (duplicated feeding) to prevent the elastic shaft as a rotary shaft of the spur 136 from receiving damages.
With the conventional inkjet recording apparatus, as described above, no restricting means is provided for restricting the movement of the spur 136, and even where such a restricting means is provided, the spur 136 is restricted by restricting the position of the elastic shaft serving as the rotary shaft of the spur 136 by means of the restricting means.
With the latter structure, however, the elastic shaft may come in contact with the restricting means where the extremely thick recording medium is fed from the feeding apparatus 101 or where multiple recording media are fed from the feeding apparatus 101, thereby exerting large shear force to the elastic shaft, and possibly damaging the elastic shaft.
Furthermore, because the restricting means for restricting the movement of the spur 136 by restricting the movement of the elastic shaft is provided only in substantially the perpendicular direction with respect to the feeding surface of the recording medium, the elastic shaft may be damaged upon exertion of shear force in a direction that the recording medium is pulled out to the elastic shaft serving as the rotary shaft of the spur 136 when, e.g., the recording medium is pulled out due to occurrence of jamming of the recording media. Therefore, it is required to make the elastic shaft itself stronger, and this requirement may result in restriction on design.
As a structure to pull out the recording medium without exerting load to the spur 136 during paper jamming, a spur 136 may be conceivably attached to a cover portion that can be opened and closed as shown in FIG. 11, but in such a case, the structure may bring higher production costs and restriction on accuracy in assembling parts.
It is an object of the invention to provide a sheet feeding apparatus capable of preventing an elastic shaft of a spur from receiving damages due to force in multiple directions exerted to the spur during paper jamming or the like.